Microelectronic elements often comprise a thin slab of a semiconductor material, such as silicon or gallium arsenide, commonly called a semiconductor chip or die. Dies are commonly provided as individual, prepackaged units. In some unit designs, the die is mounted to a substrate or a chip carrier, which is in turn mounted on a circuit panel or carrier, such as a printed circuit board (PCB).
Active circuitry is often fabricated on a first face of the die (e.g., a front surface). To facilitate electrical connection to the active circuitry, the die is provided with bond pads on the same face. The bond pads are typically placed in a regular array either around the edges of the die or, for many memory devices, in the die center. The bond pads are generally made of a conductive metal, such as copper or aluminum, and can be about 0.5 micron (μm) thick. The bond pads can include a single layer or multiple layers of metal. The size of the bond pads can vary with the device type, but often measure tens to hundreds of microns on a side.
Microelectronic elements such as semiconductor dies typically require many input and output connections to other electronic components. The input and output contacts of a die or other comparable device are generally disposed in grid-like patterns that substantially cover a surface of the die (commonly referred to as an “area array”) or in elongated rows which may extend parallel to and adjacent to each edge of the die's front surface, or in the center of the front surface. Dies can be provided in packages that facilitate handling of the die during manufacture and during mounting of the die on an external substrate such as a circuit board or other circuit panel. For example, many dies are provided in packages suitable for surface mounting. Numerous packages of this general type have been proposed for various applications. Most commonly, such packages include a dielectric element, commonly referred to as a “chip carrier” with terminals formed as plated or etched metallic structures on the dielectric. The terminals typically are connected to the contacts (e.g., bond pads) of the die by conductive features such as thin traces extending along the die carrier and by fine leads or wires extending between the contacts of the die and the terminals or traces. In a surface mounting operation, the package may be placed onto a circuit board so that each terminal on the package is aligned with a corresponding contact pad on the circuit board. Solder or other bonding material is provided between the terminals and the contact pads. The package can be permanently bonded in place by heating the assembly so as to melt or “reflow” the solder or otherwise activate the bonding material.
The input and output connections, and other thin traces making connections within the semiconductor die package may be implemented as transmission lines (such as micro-strip transmission lines, for example), which comprise conductors having a cross-section that is several to tens of microns across. Additionally, transmission lines may be used to interconnect the package to the PCB carrier, and may be used to make various other connections on the PCB carrier as well. Noise in the form of far end crosstalk (FEXT) can be induced on conductors of transmission lines from signals propagating on other nearby conductors of the circuit. This can create challenges to accurate signal transmission via the transmission lines, particularly as the scale and pitch of the transmission lines becomes finer.